Printing control device, image forming apparatus, and image forming method

ABSTRACT

A printing control device is disclosed. The printing control device includes a user interface unit to receive an print command for a print job, an extraction unit to extract a bitmap image from the print job, a sketch image generating unit to generate a sketch image by using the extracted bitmap image, a print data generating unit to replace the bitmap image by the generated sketch image in the print job to generate print data, and a communication interface unit to transmit the generated print data to an image forming apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from of Russian PatentApplication No. 2010137868, filed Sep. 13, 2010, in the Russian Agencyfor Patents and Trademark, and Korean Patent Application No.10-2011-0015092, filed Feb. 21, 2011, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Apparatuses and methods consistent with the present general inventiveconcept relate to a printing control device, an image forming apparatus,and an image forming method. More particularly, the present generalinventive concept relates to a printing control device, an image formingapparatus, and an image forming method, which can convert a bitmap imageto a sketch image in print data and print the print data in which thebitmap image is converted to the sketch image.

2. Description of the Related Art

In modern printing devices, saving of a consumption agent, inparticular, a toner, is very important and has significant ecologicalimpact. In this regard, there are a lot of patents and publicationsdevoted to draft printing or toner saving in printing devices viaspecial processing to a rendered (rasterized) image of a printed page.

A general method for printing in a draft mode is decreasing an opticaldensity for the whole image during rasterization. Forelectrophotographic and ink-jet printers, the decrease of the opticaldensity is realized by means of an increase of brightness to pixels ofrasterized graphical objects before rasterization thereof, which uses ahalftoning or a change in halftoning threshold. For example, U.S. Pat.No. 5,646,670 proposes an apparatus and a method to reduce tonerconsumption by a decrease of overall image density for color image. U.S.Pat. No. 5,946,450 describes a method to reduce toner or ink consumptionin rasterized image by a change of channel transfer function, whichreduces the image in size as a whole. U.S. Pat. No. 6,476,836 describesan image forming apparatus where image pixels having values larger thana threshold are converted into a predetermined pattern received as aresult of PWM (pulse width modulation), while for pixels of image havingvalues not larger than the threshold, no output is made.

However, the decrease of optical density for the whole page seriouslydeteriorates the printed hardcopy in quality. If the optical density forthe whole page is decreased, edges of characters in a text becomeragged, the text becomes inaccurate in shape and poor in readability,and the text is sometimes not recognizable by OCR applications, ascompared with a normal mode. In order to provide significant tonersaving, the whole printed page has to be notably impaired, for example,50% or more, in quality

At present time, a majority of printed documents contains pictures,which are stored and transferred as color or grayscale bitmaps. Forinstance, web-pages, as a rule, contain a lot of bitmaps. Printing thesebitmaps leads to a significant consumption of toner. To address thisproblem, there are several technical solutions, providing a capabilityto skip a printing of such bitmaps. For instance, US laid-open patentapplication No. 2009/0195811 describes a method for printing only textobjects from PDF.

U.S. Pat. Nos. 5,751,433 and 5,751,434 describe systems and methods fordraft printing by changing a function of channel transform in dependencefrom the type of printed object. It causes only the bitmaps to worsen inquality, and allows the text to preserve a quality thereof for draftprinting.

U.S. Pat. No. 6,972,857 describes a method for controlling a use ofconsumable on a printing device. For every page, a page cost is set, andits value depends on the number of dots to be printed. If the page costexceeds a preset threshold, at least one of known toner savingtechniques is applied.

It is necessary to note that the existing approaches for draft printingeither worsen the quality of the whole printed page or totally skip theprinting of bitmaps, which leads to important information loss. On theother hand, sometimes, if the quality of draft printing is quite high,the amount of saved toner is insignificant.

Also, the majority of proposed methods for draft printing does notprovide accurate estimation of saved toner.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present general inventive concept overcomethe above disadvantages and other disadvantages not described above.Also, the present general inventive concept is not required to overcomethe disadvantages described above, and an exemplary embodiment of thepresent general inventive concept may not overcome any of the problemsdescribed above.

The present general inventive concept provides a printing controldevice, an image forming apparatus, and an image forming method, whichcan convert a bitmap image to a sketch image in print data and print theprint data in which the bitmap image is converted to the sketch image.

Additional aspects and features of the present general inventive conceptwill be set forth in part in the description which follows and, in part,will be obvious from the description, or may be learned by practice ofthe general inventive concept.

Features of the present general inventive concept may be achieved by animage forming method that includes extracting a bitmap image from printdata, converting the extracted bitmap image to a sketch image, replacingthe bitmap image by the sketch image in the print data, and printing theprint data in which the bitmap image is replaced by the sketch image.

The method may further include estimating a percentage of resource savedaccording to the replacement of the bitmap image by the sketch image,and informing a user of the percentage of saved resource.

The converting may include enhancing a contrast of the extracted bitmapimage, converting the bitmap image with the enhanced contrast to agrayscale image, generating a mask by means of an edge detection of thegrayscale image, and multiplying each of color channels of the bitmapimage with the enhanced contrast by the mask to generate the sketchimage.

The edge detection of the grayscale image may be performed by using aDifference-of-Gaussians filter with a limitation of subsequentthreshold, and parameters and the threshold of theDifference-of-Gaussians filter may use a printing resolution and thesize of image printed on a printing paper.

On the other hand, the converting may include enhancing a contrast ofthe extracted bitmap image, blurring the bitmap image with the enhancedcontrast by using a Gaussian filter, generating a Saliency map for thebitmap image with the enhanced contrast, blending the bitmap image withthe enhanced contrast and the blurred bitmap image by using thegenerated Saliency map as an alpha channel, converting the bitmap imageresulting from blending to a grayscale image, generating a mask by meansof an edge detection of the grayscale image, and multiplying each ofcolor channels of the bitmap image with the enhanced contrast by themask.

The edge detection of the grayscale image may be performed by using aDifference-of-Gaussians filter with a limitation of subsequentthreshold, and parameters and the threshold of theDifference-of-Gaussians filter may use a printing resolution and thesize of image printed on a printing paper.

The method may further include converting the sketch image to agrayscale image by using one of the following formulas:

I=0.3r ^(˜)+0.6g ^(˜)+0.21b ^(˜),

I=(r ^(˜) +g ^(˜) +b ^(˜))/3; and

I=max(r ^(˜) ,g ^(˜) ,b ^(˜)),

where r^(˜), g^(˜), and b^(˜) are color channels of the sketch image,respectively.

The estimating the percentage of saved resource preferably includescalculating the percentage of saved printing resource by using thefollowing formula:

${E = \frac{\sum\limits_{n}{P(n)}}{{\sum\limits_{n}{P(n)}} + {\sum\limits_{i}{\left( {100/\left( {100 - {{Eb}(i)}} \right)} \right) \times {{Ns}(i)}}} - {{Ns}(i)}}},$

where E is the percentage of a saved printing resource, P(n) is thetotal number of dots used for printing all the replaced print data, i isthe number of bitmap images included in the print data, Ns(i) is thetotal number of dots used for printing an i-th sketch image, and Eb(i)is a percentage of saved resource of the i-th sketch image according thereplacement by the i-th sketch image and is calculated by the followingformula:

Eb(i)=100%×(Nb(i)−Ns(i))/Nb(i),

where Nb(i) is the total number of dots used for printing an i-th bitmapimage, and Ns(i) is the total number of dots used for printing the i-thsketch image.

The estimating the percentage of saved resource preferably includescalculating percentages of saved resources for respective printingcolors, separately.

On the other hand, the converting may further include processing thegenerated mask with a dilation filter, and the multiplying may includemultiplying each of the color channels of the bitmap image with theenhanced contrast by the mask processed with the dilation filter.

Features of the present general inventive concept may also be achievedby a printing control device connectable with an image forming apparatusincludes a user interface unit to receive a print command for a printjob, an extraction unit to extract a bitmap image from the print job, asketch image generating unit to generate a sketch image by using theextracted bitmap image, a print data generating unit to replace thebitmap image by the generated sketch image in the print job to generateprint data, and a communication interface unit to transmit the generatedprint data to the image forming apparatus.

The device preferably further includes an estimation unit to estimate apercentage of resource saved according to the replacement of the bitmapimage by the sketch image, and the user interface unit preferablydisplays the estimated percentage of saved resource.

The sketch image generating unit may include a contrast enhancing partto enhance a contrast of the extracted bitmap image, a color convertingpart to convert the bitmap image with the enhanced contrast to agrayscale image, a mask generating part to generate a mask by detectingedges of the grayscale image, and a multiplication part to multiply thebitmap image with the enhanced contrast by the mask to generate thesketch image.

The sketch image generating unit preferably further includes a blurringpart to blur the bitmap image with the enhanced contrast, a Saliency mapgenerating part to generate a Saliency map for the bitmap image with theenhanced contrast, and a blending part to blend the bitmap image withthe enhanced contrast and the blurred bitmap image by using thegenerated Saliency map as an alpha channel, and the color convertingpart preferably converts the bitmap image resulting from blending to agrayscale image.

The sketch image generating unit preferably further includes a filterpart to process the generated mask with a dilation filter, and themultiplication part preferably multiplies the bitmap image with theenhanced contrast by the mask processed with the dilation filter.

The color converting part preferably converts the generated sketch imageto a grayscale sketch image, and the print data generating unitpreferably replaces the bitmap image by the grayscale sketch image inthe print job to generate the print data.

Features of the present general inventive concept may also be achievedby an image forming apparatus includes a communication interface unit toreceive print data, an extraction unit to extract a bitmap image fromthe received print data, a sketch image generating unit to generate asketch image by using the extracted bitmap image, and an image formingunit to replace the bitmap image by the generated sketch image in thereceived print data and to print the print data with the replaced sketchimage.

The sketch image generating unit may include a contrast enhancing partto enhance a contrast of the extracted bitmap image, a color convertingpart to convert the bitmap image with the enhanced contrast to agrayscale image, a mask generating part to generate a mask by detectingedges of the grayscale image, and a multiplication part to multiply thebitmap image with the enhanced contrast by the mask to generate thesketch image.

The sketch image generating unit preferably further includes a blurringpart to blur the bitmap image with the enhanced contrast, a Saliency mapgenerating part to generate a Saliency map for the bitmap image with theenhanced contrast, and a blending part to blend the bitmap image withthe enhanced contrast and the blurred bitmap image by using thegenerated Saliency map as an alpha channel, and the color convertingpart preferably converts the bitmap image resulting from blending to agrayscale image. °

The color converting part preferably converts the generated sketch imageto a grayscale sketch image, and the image forming unit preferablyreplaces the bitmap image by the grayscale sketch image in the printdata and prints the print data with the replaced sketch image.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects of the present general inventive conceptwill become more apparent by describing certain exemplary embodiments ofthe present general inventive concept with reference to the accompanyingdrawings, in which:

FIGS. 1A to 1C are views showing examples of a bitmap image, and anexample of a sketch image converted from the bitmap image according toan exemplary embodiment of the present general inventive concept,respectively;

FIG. 2 is a flow chart illustrating an image forming method according toan exemplary embodiment of the present general inventive concept;

FIG. 3 is a flow chart concretely illustrating an example of a step ofconverting a bitmap image to a sketch image in FIG. 2;

FIG. 4 is a flow chart concretely illustrating another example of thestep of converting the bitmap image to the sketch image in FIG. 2;

FIG. 5 is a view showing examples of various threshold values to animage histogram used in performing a step of enhancing a contrast of thebitmap image in FIGS. 3 and 4;

FIG. 6 is a view concretely illustrating a Saliency map generatingoperation in FIG. 4;

FIG. 7 is a view showing a relation between a pixel value and a percentof printed dots;

FIG. 8 is a block diagram showing a construction of a printing controldevice according to an exemplary embodiment of the present generalinventive concept; and

FIG. 9 is a block diagram showing a construction of an image formingapparatus according to an exemplary embodiment of the present generalinventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present general inventive concept aredescribed in greater detail below with reference to the accompanyingdrawings.

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to the likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept while referring to thefigures.

FIG. 2 is a flow chart showing an image forming method according to anexemplary embodiment of the present general inventive concept.

Referring to FIG. 2, a bitmap image is extracted from print data first(S201). To be specific, although the print data includes texts, bitmaps,and vector graphics, only the bitmap image may be extracted from theprint data. Here, the print data may be print data, such as a pagedescription language (PDL), for example, postscript (PS), PCL, XPS, PDF,etc., which are generated in a printing control device and transmittedto an image forming apparatus, or a file or the like, which istransmitted by a direct print method. On the other hand, the extractedbitmap image may be a grayscale bitmap image or a color bitmap image. Itwill be assumed and explained below that the extracted bitmap image isthe color bitmap image.

The extracted bitmap image is converted to a sketch image (S202).Detailed descriptions on sketch image-converting operation will beexplained with reference to FIGS. 3 and 4. If the print data includes aplurality of bitmap images, a plurality of sketch image corresponding torespective bitmap images may be produced.

Next, in the print data, the bitmap image is replaced by the sketchimage (S203). The bitmap image in the print data is replaced by thesketch image generated through the process as described above togenerate a new print data. If the plurality of bitmap images is includedin the print data, they may be replaced by the corresponding bitmapimages, respectively, to generate a new print data.

Thereafter, a percentage of resource saved according to the conversionof the bitmap image by the sketch mage is estimated (S204). Inrealization, this estimation operation may be omitted. Hereinafter, amethod for estimating the percentage of saved resource will be describedin detail.

Every pixel of an image may correspond to several points on a printingpaper. A function of dependence of a percentage of points to be printedto pixel values or color intensities of respective pixels may bereceived from preliminary calibration means of the image formingapparatus. For black-and-white printing devices, this function is formedfrom one argument-pixel value. FIG. 7 shows an example of such afunction.

For color printing devices, arguments of vector with intensity values ofcolor components of the function as described above are, for example, r,g, and b values. Therefore, the number of dots to be printed for a wholebitmap image may be estimated based on the function of dependence of thepercentage of points to be printed to the pixel values or theintensities of color components. Accordingly, the percentage of savedprinting resource for the bitmap image according to the conversion ofthe bitmap image by the sketch mage may be estimated by using thefollowing mathematic formula 1:

Eb=100%×(Nb−Ns)/Nb,  [mathematic formula 1]

where Eb is the percentage of a saved printing resource, Nb is the totalnumber of dots used for printing the bitmap image, and Ns is the totalnumber of dots used for printing the sketch image.

Here, Nb and Ns may be computed using the function of dependence of thepercentage of points to be printed to the pixel values or theintensities of color components.

For color printing, the percentage of saved printing resource may becomputed separately for each color to be printed. In addition, thenumber of printed dots for whole print data and the number of printeddots for the sketch image may counted in by means of an analysis ofcertain commands in PDL and corresponding display lists, which are anexample of the print data.

The percentage of saved printing resource for the whole print dataaccording to the conversion of the bitmap image by the sketch mage maybe estimated by using the following mathematic formula 2:

$\begin{matrix}{{E = \frac{\sum\limits_{n}{P(n)}}{\begin{matrix}{{\sum\limits_{n}{P(n)}} + \sum\limits_{i}} \\{{\left( {100/\left( {100 - {{Eb}(i)}} \right)} \right) \times {{Ns}(i)}} - {{Ns}(i)}}\end{matrix}}},} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

where E is the percentage of saved printing resource for the whole printdata, i is the number of bitmap images included in the print data, P(n)is the total number of dots used for outputting all the replaced printdata, Ns(i) is the total number of dots used for outputting an i-thsketch image, and Eb(i) is a percentage of saved resource for the i-thsketch image according the conversion of an i-th bitmap image by thei-th sketch image.

Next, the print data in which the bitmap image is replaced by the sketchimage is printed (S205). For instance, if the image forming method iscarried out by a printing control device, the printing control devicemay transmit the print data with the replaced sketch image to the imageforming apparatus to print them. If the image forming method is carriedout by an image forming apparatus, the image forming apparatus maydirectly print the print data with the replaced sketch image.

Next, the computed percentage of saved resource may be displayed for auser (S206). For instance, if the image forming method is carried out bythe printing control device, the percentage of saved resource may bedisplayed through a user interface window provided on the printingcontrol device. If the image forming method is carried out by the imageforming apparatus, information on the percentage of saved resource maybe displayed through a user interface window provided on the imageforming apparatus or may be transmitted to the printing control device,so that the percentage of saved resource is displayed through the userinterface window provided on the printing control device for the user.

Hereinafter, an effect of the image forming method according to anexemplary embodiment of the present general inventive concept will beexplained with reference to FIGS. 1A 1B, and 1C.

FIG. 1A shows an example of the bitmap image 110 included in print data100, FIG. 1B shows an example of the bitmap image 120 included in theprint data 100 when conventional toner saving techniques are used, andFIG. 1C shows an example of the sketch image 130 converted from thebitmap image 110 according to an exemplary embodiment of the presentgeneral inventive concept. The print data 100 may include additionalcontent 115, such as text and graphics, that are not altered accordingto the present general inventive concept. Making a comparison betweenFIGS. 1C and 1B, it can be appreciated that toner saving rates in FIGS.1C and 1B are approximately 83% to that in the FIG. 1A, but in FIG. 1B,the bitmap image 120 itself is so blurry that the user cannot easilydistinguish contents therein, whereas in FIG. 1C, the sketch image 130is so vivid that the user easily distinguish contents therein.

Thus, the image forming method according to an exemplary embodiment ofthe present general inventive concept converts the bitmap image includedin the print data to the sketch image and outputs the print data inwhich the bitmap image is converted to the sketch image, therebyefficiently saving the resource, such as a toner or an ink, whilemaintaining discrimination for contents in the image.

Also, the image forming method according to an exemplary embodiment ofthe present general inventive concept can reliably estimate thepercentage of resource saved according to the replacement of the bitmapimage with the sketch mage and inform the user of it, thereby allowingthe user to clearly understand the effect of the draft printing and thusto exactly make a plan for consumable replacement. The image formingmethod as shown in FIG. 2 may be executed on a printing control device800 with construction of FIG. 8, an image forming apparatus 900 withconstruction of FIG. 9, or a printing control device or an image formingapparatus with any other construction.

FIG. 3 is a flow chart concretely illustrating an example of anoperation to convert the bitmap image to the sketch image in FIG. 2.Here, it will be explained that the bitmap image is a color bitmap imageand has r, g, and b channels.

First, to improve an appearance of the bitmap image and easily recognizeit, a contrast of the bitmap image is enhanced (S301).

First of all, a global histogram H of the bitmap image is calculated. Tocalculate the histogram, a color bitmap may be converted to an intensitybitmap or a grayscale bitmap. There are various methods for convertingthe color image to the grayscale image. Among these methods, thefollowing three methods are most widely used.

I=0.3r+0.6g+0.1b;  [mathematic formula 3]

I=(r+g+b)/3; and  [mathematic formula 4]

I=max(r,g,b),  [mathematic formula 5]

where r, g, and b are r, g, and b channels in the bitmap image.

To convert the color image to the grayscale image, all of the mathematicformulas 3, 4, and 5 as described above may be used. However, it isdesirable that the mathematic formula 5 is used.

A low boundary of range for contrast adjustment may be calculated byusing the following mathematic formula 6:

$\begin{matrix}{{{low} = {\min \begin{pmatrix}{T,{\min \left\{ i \middle| {{H\lbrack i\rbrack} \geq H_{0}} \right\}},} \\{\min \left\{ i \middle| {{\sum\limits_{k = 0}^{i}{H\lbrack k\rbrack}} \geq C_{0}} \right\}}\end{pmatrix}}},} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 6} \right\rbrack\end{matrix}$

where H₀ is a low threshold value for histogram level, C₀ is a lowthreshold value for histogram area and T is a threshold value forhistogram intensity. The threshold value T for histogram intensity isapplied to avoid excessive image darkening.

A high boundary of range for contrast adjustment may be calculated byusing the following mathematic formula 7:

$\begin{matrix}{{{high} = {\max \begin{pmatrix}{{\max \left\{ i \middle| {{H\lbrack i\rbrack} \geq H_{1}} \right\}},} \\{\max \left\{ i \middle| {{\sum\limits_{k = i}^{2^{n} - 1}{H\lbrack k\rbrack}} \geq C_{1}} \right\}}\end{pmatrix}}},} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

where H₁ is a high threshold value for histogram level and C₁ is a highthreshold value for histogram area. FIG. 5 illustrates examples of thethreshold values as described above.

When the low and high boundaries of range are calculated, a contrastenhancement for each of the r, g, and b color channels may be performedusing the following mathematic formulas 8, 9, and 10:

r′=255×(r−low)/(high−low);  [mathematic formula 8]

g′=255×(g−low)/(high−low); and  [mathematic formula 9]

b′=255×(b−low)/(high−low).  [mathematic formula 10]

Here, r′, g′, and b′ refer to the r, g, and b color channels havingenhanced contrast. Next, the bitmap image with the enhanced contrast isconverted to a grayscale image (S302). The bitmap image in which thecontrast is enhanced using one of the mathematic formulas 3, 4, and 5 asdescribed above may be converted to the grayscale image. In the presentembodiment, although the bitmap image is explained as being converted tothe grayscale image using only the mathematic formulas 3, 4, and 5, thepresent general inventive concept is not limited thereto. For instance,in realization, the bitmap image with the enhanced contrast may beembodied in such a manner that it is converted to the grayscale image byusing any method other than the mathematic formulas 3, 4, and 5.

Thereafter, a mask is generated by means of an edge detection to thegrayscale image (S303). The mask may be generated by using aDifference-of-Gaussians (DOG) filter with subsequent threshold to detectedges of the grayscale image, as in the following mathematic formula 11.In the present embodiment, although the mask is explained as beinggenerated by using the DOG filter, the present general inventive conceptis not limited thereto. For instance, in realization, the mask may beembodied in such a manner that it is generated by using any other edgedetection method.

$\begin{matrix}{{{{G_{\sigma_{1}}\left( {x,y} \right)} = {\frac{1}{\sqrt{2\pi \; \sigma_{1}^{2}}}^{- \frac{x^{2} + y^{2}}{2\sigma_{1}^{2}}}}};}{{{G_{\sigma_{2}}\left( {x,y} \right)} = {\frac{1}{\sqrt{2\pi \; \sigma_{2}^{2}}}^{- \frac{x^{2} + y^{2}}{2\sigma_{2}^{2}}}}};{and}}{M = \left\{ \begin{matrix}{1,} & {\left( {{I^{*}G_{\sigma_{1}}} - {I^{*}G_{\sigma_{2}}}} \right) < T} \\{0,} & {{otherwise},}\end{matrix} \right.}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 10} \right\rbrack\end{matrix}$

where I is the grayscale image, T is a threshold value, * is aconvolution. DOG filter parameters σ1, σ2, and the threshold value Tdepend on a printing resolution and the size of image printed on aprinting paper.

Next, a sketch image is created by multiplication of the bitmap imagewith the enhanced contrast by the generated mask (S304). The sketchimage may be created by multiplying each of color channels of the bitmapimage with the enhanced contrast by the generated mask, as in thefollowing mathematic formulas 12, 13, and 14.

r ^(˜) =r′×M  [mathematic formula 12]

g ^(˜) =g′×M  [mathematic formula 13]

b ^(˜) =b′×M [mathematic formula 14]

Here, the values r˜, g˜, and b˜ correspond to the r, g, and b channelshaving the enhanced contrast and sketch characteristics. The approach ofcreating the sketch image as described above is suitable for most bitmapimages and produces a sketch image having good visual characteristics,thereby allowing the user to easily recognize the created sketch image.

However, for some images with contrast or textured background, sketchimages created by the approach as described above may have too manycontours, which may lead to a decline in resource saving and maycomplicate image recognizability. To overcome this drawback, an improvedbitmap-to-sketch conversion approach is proposed. This approach is basedon using of an Importance map or a Saliency map. Hereinafter, anoperation of converting to the bitmap image to the sketch image by usingthe Importance map and the Saliency map is described with reference toFIG. 4.

FIG. 4 is a flow chart concretely illustrating another example of theoperation to convert the bitmap image to the sketch image in FIG. 2.

First, a contrast of the bitmap image is enhanced (S401). Since thiscontrast enhancing operation is the same as that in the step S301 ofFIG. 3, detailed description thereof will be omitted.

Next, the bitmap image with the enhanced contrast is blurred (S402). Tobe specific, as in the mathematic formulas 16, 17, and 18, each of r′,g′, and b′ color channels of the bitmap image with the enhanced contrastis convoluted with a Gaussian filter value as shown in the followingmathematic formula 15, so that a blurring for the bitmap image with theenhanced contrast is performed.

$\begin{matrix}{{G_{\sigma}\left( {x,y} \right)} = {\frac{1}{\sqrt{2\pi \; \sigma^{2}}}^{- \frac{x^{2} + y^{2}}{2\sigma^{2}}}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 15} \right\rbrack \\{r_{b} = {r^{\prime*}G_{\sigma}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 16} \right\rbrack \\{g_{b} = {g^{\prime*}G_{\sigma}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 17} \right\rbrack \\{b_{b} = {b^{\prime*}G_{\sigma}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 18} \right\rbrack\end{matrix}$

Here, r_(b), g_(b), and b_(b) correspond to the r, g, and b channelshaving a blurred characteristic. Thereafter, a Saliency map for thebitmap image with the enhanced contrast is built (S403). The Saliencymap may be built using an approach as shown in FIG. 6. Hereinafter, anoperation of building the Saliency map will be explained with referenceto FIG. 6.

First, an intensity map and four color channels R, G, B, and Y for thebitmap image with the enhanced contrast are built. The intensity map maybe built by applying any one of the mathematic formulas 3, 4, and 5 asdescribed above to the bitmap image with the enhanced contrast, and thefour color channels may be computed through the following mathematicformulas 19, 20, 21, and 22:

$\begin{matrix}{{R = {r^{\prime} - \frac{g^{\prime} + b^{\prime}}{2}}},} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 19} \right\rbrack \\{{G = {g^{\prime} - \frac{r^{\prime} + b^{\prime}}{2}}},} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 20} \right\rbrack \\{{B = {b^{\prime} - \frac{r^{\prime} + g^{\prime}}{2}}},{and}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 21} \right\rbrack \\{Y = {\frac{r^{\prime} + g^{\prime}}{2} - \frac{\left. {r^{\prime} - g^{\prime}} \right\rceil}{2} - {b^{\prime}.}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 22} \right\rbrack\end{matrix}$

And then, 8-level Gaussian pyramids are constructed using the four colorchannels computed by the mathematic formulas 19, 20, 21, and 22 asdescribed above and 8-level Gabor pyramids for orientations θε{0, 45,90, 135} are created using the built intensity map.

By an operation of center difference of two maps, one of which is nameda central (good) map, the scale of which is designated as c, and theother of which is named a surround (rough) map, the scale of which isdesignated as s, characteristic maps may be generated from the followingmathematic formulas 23, 24, 25, and 26:

I(c,s)=∥I(c)−I(s)|,  [mathematic formula 23]

RG(c,s)=|(R(c)−G(c))−(G(s)−R(s))|,  [mathematic formula 24]

BY(c,s)=|(B(c)−Y(c))−(Y(s)−B(s))|, and  [mathematic formula 25]

O(c,s,θ)=|O(c,θ)−O(s,θ)|,  [mathematic formula 26]

where cε{2, 3, 4} and s=C+δ, δε{2, 3}.

By the calculation as described above, the characteristic maps aregenerated as a result of difference of the central map and the surroundmap, the scales of which are reduced to the scale of the central map.

For each characteristic map, a visibility map may be created usingcentral summation operation and normalization as in the followingmathematic formulas 27, 28, and 29. The central summation consists inreducing of each map to a specified scale and a by-point summation.

$\begin{matrix}{\mspace{79mu} {\overset{\_}{I} = {\sum\limits_{c = 2}^{4}{\sum\limits_{s = {c + 3}}^{c + 4}{N\left( {I\left( {c,s} \right)} \right)}}}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 27} \right\rbrack \\{\overset{\_}{C} = {\sum\limits_{c = 2}^{4}{\sum\limits_{s = {c + 3}}^{c + 4}\left\lbrack {{N\left( {{RG}\left( {c,s} \right)} \right)} + {N\left( {{BY}\left( {c,s} \right)} \right)}} \right\rbrack}}} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 28} \right\rbrack \\{\overset{\_}{O} = {\sum\limits_{\theta \in {\{{0,45,90,135}\}}}{N\left( {\sum\limits_{c = 2}^{4}{\sum\limits_{s = {c + 3}}^{c + 4}{N\left( {O\left( {c,s,\theta} \right)} \right)}}} \right)}}} & \left\lbrack {{mathematic}{\mspace{11mu} \;}{formula}\mspace{14mu} 29} \right\rbrack\end{matrix}$

Here, N( ) is a normalization operator.

The normalization operator consists of two parts. To be specific, atfirst, a Gaussian filter is applied in order to decrease noises andrandom peaks, and then an average local maximum (ALM) is computed. Aftercomputation of the average local maximum, the whole image is multipliedby the value. An application of such a normalization method allows verybright background to be neglected in the Saliency map, and leaves onlythe more important sites, which have not been masked by raisedbrightness.

Next, orientation maps Ō related to the orientation, color maps Crelated to the color, and intensity maps Ī related to the intensity aresummed with weights into a final image which is called the saliency mapS, as in the following mathematic formula 30:

$\begin{matrix}{{S = \frac{\begin{matrix}{{{wI} \cdot {N\left( \overset{\_}{I} \right)}} +} \\{{{wC} \cdot {N\left( \overset{\_}{C} \right)}} + {{wO} \cdot {N\left( \overset{\_}{O} \right)}}}\end{matrix}}{{wI} + {wC} + {wO}}},} & \left\lbrack {{mathematic}\mspace{14mu} {formula}\mspace{14mu} 30} \right\rbrack\end{matrix}$

where wI is a weight for intensity map, wO is a weight for orientationmap, and wC is a weight for intensity map.

Since information about the brightness and the orientation is moreimportant than color information, the weights may be set and used inrelations wI=wO=2 and wC=1. Further, S is normalized to range from 0 to1.

In the exemplary embodiment, although the operation is explained asbuilding the Saliency map in the approach as shown in FIG. 6, thepresent general inventive concept may build the Saliency map by anyother approaches. For instance, an approach for Saliency map buildingdescribed on the paper “Efficient Construction of Saliency Map” byWen-Fu Lee, Tai-Hsiang Huang, Yi-Hsin Huang, Mei-Lan Chu, and Horner H.Chen (SPIE-IS&T/Vol. 7240, 2009) may be used.

Referring again to FIG. 4, when the Saliency map is built, the bitmapimage with the enhanced contrast and the blurred bitmap image areblended using the built Saliency map as an alpha channel (S404). Theblending of the bitmap image with the enhanced contrast and the blurredbitmap image are performed using the following mathematic formulas 31,32, and 33:

r ₁ =S×r′+(1−S)×r _(b)  [mathematic formula 31]

g ₁ =S×g′+(1−S)×g _(b), and  [mathematic formula 32]

b ₁ =S×b′+(1−S)×b _(b)  [mathematic formula 33]

Such a process allows a background in the bitmap image to blur andprevents the sketch image from occurring unnecessary lines thereon.

And then, the blended image is converted to a grayscale image (S405).The conversion of the blended image to the grayscale image may beperformed using the any one of the mathematic formulas 3, 4, and 5 asdescribed above.

Thereafter, a mask is generated by means of an edge detection on thegrayscale image (S406). Since this operation of generating the mask isthe same as the step (S303) as described above, a detailed descriptionthereof will be omitted.

Next, the generated mask is processed with a morphological dilationfilter (S407). Here, structural elements of the dilation filter may bevaried according to an image forming apparatus and a resolution thereof.Also, this step is optional.

Finally, the bitmap image is multiplied by the generated mask to createa sketch image (S408). The sketch image may be created by multiplyingeach of color channels of the bitmap image with the enhanced contrast bythe generated mask, as in the following mathematic formulas 34, 35, and36:

r ^(˜) =r ₁ ′×M;  [mathematic formula 34]

g ^(˜) =g ₁ ′×M; and  [mathematic formula 35]

b ^(˜) =b ₁ ′×M,  [mathematic formula 36]

where r1′, g1′, and b1′ are r, g, and b color channels of the bitmapimage with the enhanced contrast, respectively, M is the mask, andr^(˜), g^(˜)and b^(˜) are r, g, and b color channels of the sketchimage, respectively.

If the sketch image is created by the approach as described above, itcan be created in such a form that even for the image with contrast ortextured background, the counter thereof is properly adjusted.

On the other hand, the created color sketch image may be converted to agrayscale sketch image by using one of the following mathematic formulas37, 38, and 39, so that it is used.

I=0.3r ^(˜)+0.6g ^(˜)+0.1b ^(˜)  [mathematic formula 37]

I=(r ^(˜) +g ^(˜) +b ^(˜))/3  [mathematic formula 38]

I=max(r ^(˜) ,g ^(˜) ,b ^(˜))  [mathematic formula 39]

If the color sketch image is converted to the grayscale sketch image,the percentage of saved resource can be improved.

FIG. 8 is a block diagram showing a construction of a printing controldevice according to an exemplary embodiment of the present generalinventive concept.

Referring to FIG. 8, the printing control device 800 may include acommunication interface unit 810, a storing unit 820, a user interfaceunit 830, an extraction unit 840, a sketch image generating unit 850, aprint data generating unit 860, an estimation unit 870, and control unit880.

The user interface unit 830 has a plurality of function keys with whichthe user can set or select a variety of functions provided by theprinting control device 800, and receives a print command for a printjob from the user. Further, the user interface unit 830 may be embodiedby a device, such as a touchpad or the like, capable of simultaneouslyimplementing inputs and outputs, and embodied combining an input device,such as a mouse, a keyboard and the like, and a display device, such aCRT monitor, a LCD monitor, LED or the like.

The storing unit 820 may store print jobs. Here, the print job may be afile, for example, a document file or a web page, including contents,such as a text, a bitmap image and a vector graphic. Further, thestoring unit 820 may store print data generated at a print driverprovided on the printing control device 800 or a print date generated atthe print data generating unit 860 to be described later.

On the other hand, the storing unit 820 may be embodied by a storingmedium in the printing control device 800 and an outer storing medium,for example, a removable disk including a universal serial bus (USB)memory, a storing medium connected to a host, a web server connectedthrough a network, etc.

The communication interface unit 810 is provided for connecting theprinting control device 800 with the image forming apparatus 10, and maybe formed in a form connected by wire or wireless through a local areanetwork (LAN) and an internet network, or a form connected through a USBport. Further, the communication interface unit 810 may transmit theprint data generated at the print data generating unit 860 to the imageforming apparatus 10.

The extraction unit 840 extracts a bitmap image from the print job. Theextraction unit 840 may extract the bitmap image among a variety ofcontents included in the print job. Further, if a plurality of bitmapimages is included in the print job, the extraction unit 840 may extractthe plurality of bitmap images included in the print job. The extractionunit 840 may comprise a processor, memory, and control logic, and mayinclude programs and drivers stored in memory and executed by aprocessor. The processor may be part of the control unit 880, and theextraction unit 840 may include programs stored in the storing unit 820,or the extraction unit 840 may comprise separate components from thecontrol unit 880 and storing unit 820.

The sketch image generating unit 850 generates a sketch image using theextracted bitmap image. The sketch image generating unit 850 may includea contrast enhancing part 851, a color converting part 852, a maskgenerating part 853, a multiplication part 854, a blurring part 855, aSaliency map generating part 856, a blending part 857, and a filter part858. The sketch image generating unit 850 may comprise a processor,memory, and control logic, and may include programs and drivers storedin memory and executed by a processor. The processor may be part of thecontrol unit 880, and the sketch image generating unit 850 may includeprograms stored in the storing unit 820, or the sketch image generatingunit 850 may comprise separate components from the control unit 880 andstoring unit 820.

The contrast enhancing part 851 enhances a contrast of the extractedbitmap image. Since the approach of enhancing the contrast is previouslyexplained with referenced to the step S301 of FIG. 3, a detaileddescription thereof will be omitted.

The color converting part 852 converts the bitmap image with theenhanced contrast to a grayscale image. The color converting part 852may convert the bitmap image with the enhanced contrast to the grayscaleimage by using one of the mathematic formulas 3, 4, and 5 as describedabove.

Further, if the blending part 857 to be described later generates ablended bitmap image, the color converting part 852 may convert theblended bitmap image to a grayscale image.

Also, the color converting part 852 may convert a sketch image generatedat the multiplication part 858 to be described later to a grayscalesketch image. The color converting part 852 may convert the sketch imagegenerated at the multiplication part 858 to the grayscale sketch imageby using one of the mathematic formulas 37, 38, and 39 as describedabove.

The mask generating part 853 generates a mask by detecting edges of thegrayscale image. The mask generating part 853 may generate the mask bydetecting edges of the grayscale image generated at the color convertingpart 852 by using a Difference-of-Gaussians (DOG) filter with alimitation of subsequent threshold, as in the mathematic formula 11 asdescribed above.

The multiplication part 854 multiplies the bitmap image with theenhanced contrast by the mask to generate the sketch image. Themultiplication part 854 may generate the sketch image by multiplyingeach of color channels of the bitmap image with the enhanced contrast bythe mask generated at the mask generating part 853, as in the mathematicformulas 12, 13, and 14 as described above.

Further, the multiplication part 854 may generate a sketch image bymultiplying each of the color channels of the bitmap image with theenhanced contrast by a mask processed with a dilation filter at thefilter part 858.

The blurring part 855 blurs the bitmap image with the enhanced contrast.The blurring part 855 may perform a blurring of the bitmap image withthe enhanced contrast by convoluting each of r′, g′, and b′ colorchannels of the bitmap image with the enhanced contrast with theGaussian filter value as shown in the mathematic formula 15, as in themathematic formulas 16, 17, and 18 as described above.

The Saliency map generating part 856 generates a Saliency map for thebitmap image with the enhanced contrast. Since the concrete operation ofgenerating the Saliency map was previously explained in detail withreferenced to FIG. 6, a detailed description thereof will be omittedhere.

The blending part 857 blends the bitmap image with the enhanced contrastand the blurred bitmap image by using the generated Saliency map as analpha channel. The blending part 857 may blend the bitmap image with theenhanced contrast and the blurred bitmap image by using the mathematicformulas 31, 32, and 33 as described above.

The filter part 858 processes the generated mask with the dilationfilter.

The print data generating unit 860 replaces the bitmap image by thegenerated sketch image in the print job to generate print data. Theprint data generating unit 860 may replace the bitmap image in the printjob by the sketch image generated at the sketch image generating unit850, and generate the print data in which the bitmap image is replacedby the sketch image. The generated print data may have a form of one ofpostscript (PS), PCL, XPS, and PDF. If a plurality of bitmap images isincluded in the print job, the print data generating unit 860 mayreplace the plurality of bitmap images included in the print job by thecorresponding sketch images, respectively, and generate the print data.This print data generating unit 860 may be a printer driver. In anexemplary embodiment, although the extraction unit 840, the sketch imagegenerating unit 850, the print date generating unit 860 and theestimation unit 870 are explained as being separately formed, they maybe embodied by a single component, for example, a printer driver,executed by a processor and control logic circuitry, in which allconstructions thereof are included.

The estimation unit 870 estimates a percentage of resource savedaccording to the replacement of the bitmap image by the sketch image.Since the approach of estimating the percentage of saved resource ispreviously explained with referenced to FIG. 2, a detailed descriptionthereof will be omitted.

The control unit 880 may control a variety of components included in theprinting control device 800. When the control unit 880 receives theprint command for the print job from the user, it controls theextraction unit 840 and the sketch image generating unit 850 to extractthe bitmap image from the selected print job and to convert theextracted bitmap image to the sketch image, respectively. And then, whenthe sketch image is generated, the control unit 880 controls the printdata generating unit 860 to replace the bitmap image by the sketch imagein the print data thus to generate the print data in which the bitmapimage is replaced by the sketch image, and controls the communicationinterface unit 810 to transmit and print the generated print data to andin the image forming apparatus 10.

Further, the control unit 880 may control the estimation unit 870 toestimate the percentage of saved resource according to the replacementof the bitmap image by the sketch image and control the user interfaceunit 830 to display the estimated of saved resource and thus to informthe user of it.

As described above, the printing control device 800 according to anexemplary embodiment of the present general inventive concept convertsthe bitmap image included in the print job to the sketch image andoutputs the print data in which the bitmap image is converted to thesketch image, thereby efficiently saving the resource, such as the toneror the ink, while maintaining differentiation among contents in theimage.

FIG. 9 is a block diagram showing a construction of the image formingapparatus according to an exemplary embodiment of the present generalinventive concept.

Referring to FIG. 9, the image forming apparatus 900 may include a userinterface unit 910, a storing unit 920, a communication interface unit930, an extraction unit 940, a sketch image generating unit 950, animage forming unit 960, an estimation unit 970, and a control unit 980.

The user interface unit 910 has a plurality of function keys with whichthe user can set or select a variety of functions provided by the imageforming apparatus 900, and may display a percentage of saved resourceestimated by the estimation unit 970 to be described later. The userinterface unit 910 may be embodied by a device, such as a touchpad orthe like, capable of simultaneously implementing inputs and outputs, andembodied combining an input device, such as a mouse, a keyboard and thelike, and a display device, such a CRT monitor, a LCD monitor, LED orthe like.

The storing unit 920 may store print data. The storing unit 920 maystore a print date received through the communication interface unit 930to be described later. Here, the print data may be a page documentlanguage (PDL), such as postscript (PS), PCL, XPS, PDF, etc., or adocument file transmitted by a direct print method. Further, the storingunit 920 may be embodied by a storing medium in the image formingapparatus 900 and an outer storing medium, for example, a removable diskincluding a universal serial bus (USB) memory, a storing mediumconnected to a host, a web server connected through a network, etc.

The communication interface unit 930 is provided to connect the imageforming apparatus 900 with a printing control device 20, and may beconnected through a USB port, as well as by wire or wirelessly through alocal area network (LAN) and an internet network. Further, thecommunication interface unit 930 may receive the print data from theprinting control unit 20, and may receive the document file in thedirect print method. Also, the communication interface unit 930 maytransmit information for a percentage of saved resource estimated at theestimation unit 970 to be described later to the printing control device20.

The extraction unit 940 extracts a bitmap image from the print data. Theextraction unit 940 may extract the bitmap image among a variety ofcontents included in the print data. Further, if a plurality of bitmapimages is included in the print data, the extraction unit 940 mayextract the plurality of bitmap images included in the print data. Theextraction unit 940 may comprise a processor, memory, and control logic,and may include programs and drivers stored in memory and executed by aprocessor. The processor may be part of the control unit 980, and theextraction unit 940 may include programs stored in the storing unit 920,or the extraction unit 940 may comprise separate components from thecontrol unit 980 and storing unit 920.

The sketch image generating unit 950 generates a sketch image using theextracted bitmap image. The sketch image generating unit 950 may includea contrast enhancing part 951, a color converting part 952, a maskgenerating part 953, a multiplication part 954, a blurring part 955, aSaliency map generating part 956, a blending part 957, and a filter part958. The sketch image generating unit 950 may comprise a processor,memory, and control logic, and may include programs and drivers storedin memory and executed by a processor. The processor may be part of thecontrol unit 980, and the sketch image generating unit 950 may includeprograms stored in the storing unit 920, or the sketch image generatingunit 950 may comprise separate components from the control unit 980 andstoring unit 920.

The contrast enhancing part 951 enhances a contrast of the extractedbitmap image. Since the approach of enhancing the contrast waspreviously explained with referenced to the step S301 of FIG. 3, adetailed description thereof will be omitted here.

The color converting part 952 converts the bitmap image with theenhanced contrast to a grayscale image. The color converting part 952may convert the bitmap image with the enhanced contrast to the grayscaleimage by using one of the mathematic formulas 3, 4, and 5 as describedabove.

Further, if the blending part 957 to be described later generates ablended bitmap image, the color converting part 952 may convert theblended bitmap image to a grayscale image.

Also, the color converting part 952 may convert a sketch image generatedat the multiplication part 958 to be described later to a grayscalesketch image. The color converting part 952 may convert the sketch imagegenerated at the multiplication part 958 to the grayscale sketch imageby using one of the mathematic formulas 37, 38, and 39 as describedabove.

The mask generating part 953 generates a mask by detecting edges of thegrayscale image. The mask generating part 953 may generate the mask bydetecting edges of the grayscale image generated at the color convertingpart 952 by using a Difference-of-Gaussians (DOG) filter with alimitation of subsequent threshold, as in the mathematic formula 11 asdescribed above.

The multiplication part 954 multiplies the bitmap image with theenhanced contrast by the mask to generate the sketch image. Themultiplication part 954 may generate the sketch image by multiplies eachof color channels of the bitmap image with the enhanced contrast by themask generated at the mask generating part 953, as in the mathematicformulas 12, 13 and 14 as described above.

Further, the multiplication part 954 may generate a sketch image bymultiplying each of the color channels of the bitmap image with theenhanced contrast by a mask processed with a dilation filter at thefilter part 958 to be described later. The multiplication part 954 maygenerate the sketch image by multiplying each of the color channels ofthe bitmap image with the enhanced contrast by the mask generated at themask generating part 953, as in the mathematic formulas 34, 35, and 36as described above.

The blurring part 955 blurs the bitmap image with the enhanced contrast.The blurring part 955 may perform a blurring for the bitmap image withthe enhanced contrast by convoluting each of r′, g′, and b′ colorchannels of the bitmap image with the enhanced contrast with theGaussian filter value as shown in the mathematic formula 15, as in themathematic formulas 16, 17, and 18 as described above.

The Saliency map generating part 956 generates a Saliency map for thebitmap image with the enhanced contrast. Since the concrete operation ofgenerating the Saliency map is previously explained in detail withreferenced to FIG. 6, a detailed description thereof will be omitted.

The blending part 957 blends the bitmap image with the enhanced contrastand the blurred bitmap image by using the generated Saliency map as analpha channel. The blending part 957 may blend the bitmap image with theenhanced contrast and the blurred bitmap image by using the mathematicformulas 31, 32 and 33 as described above.

The filter part 958 processes the generated mask with the dilationfilter.

The image forming unit 960 replaces the bitmap image by the generatedsketch image in the print data and prints the print data. The imageforming unit 960 may replace the bitmap image in the print job by thesketch image generated at the sketch image generating unit 950, andprint the print data in which the bitmap image is replaced by the sketchimage. Further, if a plurality of bitmap images is included in the printdata, the image forming unit 960 may replace the plurality of bitmapimages included in the print data by the corresponding sketch images,respectively, and print the print data in which the plurality of bitmapimages is replaced by the corresponding sketch images, respectively. Inthe exemplary embodiment, although the extraction unit 940, the sketchimage generating unit 950, the image forming unit 960 and the estimationunit 970 are explained as being separately formed, they may be embodiedby a single component, for example, a raster image processor (RIP) inwhich all constructions thereof are included, in the image formingapparatus.

The estimation unit 970 may estimate a percentage of resource savedaccording to the replacement of the bitmap image by the sketch image.Since an approach of estimating the percentage of saved resource waspreviously explained with referenced to FIG. 2, a detailed descriptionthereof will be omitted here.

The control unit 980 may control a variety of components included in theimage forming apparatus 900. When the control unit 980 receives theprint data from the printing control device 20, it controls theextraction unit 940 and the sketch image generating unit 950 to extractthe bitmap image from the received print data and to convert theextracted bitmap image to the sketch image, respectively. And then, whenthe sketch image is generated, the control unit 980 controls the imageforming unit 960 to print the print data in which the bitmap image isreplaced by the sketch image.

Further, the control unit 980 may control the estimation unit 970 toestimate the percentage of saved resource according to the replacementof the bitmap image by the sketch image and control the user interfaceunit 910 to display the estimated of saved resource and thus to informthe user of it, or to transmit information on the estimated percentageof saved resource to the printing control device 20.

As is apparent from the foregoing description, the image formingapparatus 900 converts the bitmap image included in the print data tothe sketch image and prints the print data in which the bitmap image isconverted to the sketch image, thereby efficiently saving the resource,such as the toner or the ink, while maintaining the discrimination forcontents in the image.

Although the present general inventive concept has been illustrated andexplained by the exemplary embodiments, it is not limited to theforegoing exemplary embodiments. The present teaching can be readilyapplied to other types of apparatuses and many alternatives,modifications, and variations will be apparent to those skilled in theart. Thus, the scope of the present general inventive concept is not tobe construed as being limited to the description of the exemplaryembodiments, and is to be construed by the attached claims andequivalents.

What is claimed is:
 1. An image forming method, comprising: extracting abitmap image from print data; converting the extracted bitmap image to asketch image; replacing the bitmap image with the sketch image in theprint data; and printing the print data in which the bitmap image isreplaced with the sketch image.
 2. The method of claim 1, furthercomprising: estimating a percentage of a printing resource saved byreplacing the bitmap image with the sketch image; and informing a userof the estimated percentage of the saved printing resource.
 3. Themethod of claim 2, wherein the estimating the percentage of savedresource comprises calculating the percentage of saved printing resourceby using the following formula:${E = \frac{\sum\limits_{n}{P(n)}}{{\sum\limits_{n}{P(n)}} + {\sum\limits_{i}{\left( {100/\left( {100 - {{Eb}(i)}} \right)} \right) \times {{Ns}(i)}}} - {{Ns}(i)}}},$where E is the percentage of the saved printing resource P(n) is thetotal number of dots used for printing all the replaced print data, i isthe number of bitmap images included in the print data, Ns(i) is thetotal number of dots used for printing an i-th sketch image, and Eb(i)is a percentage of saved resource for the i-th sketch image accordingthe replacement by the i-th sketch image and is calculated by thefollowing formula:Eb(i)=100%×(Nb(i)−Ns(i))/Nb(i), where Nb(i) is the total number of dotsused for printing an i-th bitmap image, and Ns(i) is the total number ofdots used for printing the i-th sketch image.
 4. The method of claim 2,wherein the estimating the percentage of saved printing resourcecomprises separately calculating percentages of saved printing resourcesfor respective printing colors.
 5. The method of claim 1, wherein theconverting the extracted bitmap image comprises: enhancing a contrast ofthe extracted bitmap image; blurring the bitmap image with the enhancedcontrast by using a Gaussian filter; generating a Saliency map for thebitmap image with the enhanced contrast; blending the bitmap image withthe enhanced contrast and the blurred bitmap image by using thegenerated Saliency map as an alpha channel; converting the bitmap imageresulting from blending to a grayscale image; generating a mask by meansof an edge detection of the grayscale image; and multiplying each ofcolor channels of the bitmap image having the enhanced contrast by themask.
 6. The method of claim 5, wherein the detecting the edges of thegrayscale image is performed by using a Difference-of-Gaussians filterwith a limitation of subsequent threshold, and wherein parameters andthe threshold of the Difference-of-Gaussians filter use a printingresolution and the size of image printed on a printing paper.
 7. Themethod of claim 5, wherein the converting further comprises processingthe generated mask M with a dilation filter, wherein the multiplyingcomprises multiplying each of the color channels of the bitmap imagewith the enhanced contrast by the mask processed with the dilationfilter.
 8. The method of claim 1, wherein the converting the extractedbitmap image comprises: enhancing a contrast of the extracted bitmapimage; converting the bitmap image with the enhanced contrast to agrayscale image; generating a mask by means of an edge detection of thegrayscale image; and multiplying each of color channels of the bitmapimage having the enhanced contrast by the mask to generate the sketchimage.
 9. The method of claim 8, wherein the edge detection is performedby using a Difference-of-Gaussians filter with a limitation ofsubsequent threshold, and wherein parameters and the threshold of theDifference-of-Gaussians filter use a printing resolution and the size ofimage printed on a printing paper.
 10. The method of claim 1, furthercomprising: converting the sketch image to a grayscale image by usingone of the following formulas:I=0.3r ^(˜)+0.6g ^(˜)+0.21b ^(˜),I=(r ^(˜) +g ^(˜) +b ^(˜))/3; andI=max(r ^(˜) ,g ^(˜) ,b ^(˜)), where r^(˜), g^(˜), and b^(˜) are colorchannels of the sketch image, respectively.
 11. A printing controldevice to be connected to an image forming apparatus, comprising: anextraction unit to extract a bitmap image from a print job; a sketchimage generating unit to generate a sketch image by using the extractedbitmap image; a print data generating unit to replace the bitmap imagewith the generated sketch image in the print job to generate print data;and a communication interface unit to transmit the generated print datato the image forming apparatus.
 12. The device of claim 11, furthercomprising: an estimation unit to estimate a percentage of a printingresource saved according to the replacement of the bitmap image by thesketch image; and a user interface unit to display the estimatedpercentage of saved printing resource.
 13. The device of claim 11,wherein the sketch image generating unit comprises: a contrast enhancingpart to enhance a contrast of the extracted bitmap image; a colorconverting part to convert the bitmap image with the enhanced contrastto a grayscale image; a mask generating part to generate a mask bydetecting edges of the grayscale image; and a multiplication part tomultiply the bitmap image having the enhanced contrast by the mask togenerate the sketch image.
 14. The device of claim 13, wherein thesketch image generating unit further comprises: a blurring part to blurthe bitmap image with the enhanced contrast; a Saliency map generatingpart to generate a Saliency map for the bitmap image with the enhancedcontrast; and a blending part to blend the bitmap image with theenhanced contrast and the blurred bitmap image by using the generatedSaliency map as an alpha channel, and wherein the color converting partconverts the bitmap image resulting from blending to a grayscale image.15. The device of claim 14, wherein the sketch image generating unitfurther comprises a filter part to process the generated mask with adilation filter, and wherein the multiplication part multiplies thebitmap image having the enhanced contrast by the mask processed with thedilation filter.
 16. The device of claim 13, wherein the colorconverting part converts the generated sketch image to a grayscalesketch image, and wherein the print data generating unit replaces thebitmap image by the grayscale sketch image in the print job to generatethe print data.
 17. An image forming apparatus comprising: acommunication interface unit to receive print data; an extraction unitto extract a bitmap image from the received print data; a sketch imagegenerating unit to generate a sketch image by using the extracted bitmapimage; and an image forming unit to replace the bitmap image by thegenerated sketch image in the received print data and to print the printdata with the replaced sketch image.
 18. The apparatus of claim 17,wherein the sketch image generating unit comprises: a contrast enhancingpart to enhance a contrast of the extracted bitmap image; a colorconverting part to convert the bitmap image with the enhanced contrastto a grayscale image; a mask generating part to generate a mask bydetecting edges of the grayscale image; and a multiplication part tomultiply the bitmap image with the enhanced contrast by the mask togenerate the sketch image.
 19. The apparatus of claim 18, wherein thesketch image generating unit further comprises: a blurring part to blurthe bitmap image with the enhanced contrast; a Saliency map generatingpart to generate a Saliency map for the bitmap image with the enhancedcontrast; and a blending part to blend the bitmap image with theenhanced contrast and the blurred bitmap image by using the generatedSaliency map as an alpha channel, and wherein the color converting partconverts the bitmap image resulting from blending to a grayscale image.20. The apparatus of claim 18, wherein the color converting partconverts the generated sketch image to a grayscale sketch image, andwherein the image forming unit replaces the bitmap image by thegrayscale sketch image in the print data and prints the print data withthe replaced sketch image.